In the preparation of hygiene articles, such as baby diapers or sanitary towels, absorbing materials are used in order to absorb aqueous fluids. In order to prevent direct contact with the absorbing material upon wearing and to increase the wear comfort, this material is covered with a thin, water-pervious nonwoven. Nonwoven materials of this type are usually prepared from synthetic fibers, such as polyolefin or polyester fibers, because these fibers can be produced at low cost, have good mechanical properties, and are thermally stable.
In the hygiene article sector, nonwoven materials of this type are increasingly provided with skin-friendly lotions in order to generally improve tolerability and wear comfort. For example, DE 33 09 530 C1 describes a hygienic absorption liner impregnated with a skincare material which consists of triglycerides and/or partial glycerides of coconut oil fatty acids having 8 to 18 carbon atoms. In order that these preparations can transfer from the nonwoven to the skin without problems while being worn, the triglyceride and partial glyceride mixtures of DE 33 09 530 are chosen such that they have a rise point in the range from 35° C. to 40° C.
Another approach to transferring skincare substances to the skin during the wearing of hygiene articles is given in WO 96/16682. This describes a diaper whose inner covering web is prepared with a lotion which is solid or semisolid at 20° C. and which transfers to the skin of the wearer while being worn. These lotions comprise from 10% to 95% of an anhydrous emollient, which has to be plastic or liquid at room temperature, and 5% to 90% of a so-called immobilizer which is to have a melting point of at least 35° C., but preferably 40° C.
However, the main problem of the known lotions is their storage stability. It is preferable that the lotions themselves are in a form at skin temperature, i.e., approximately 36° C. to 38° C., such that they transfer to the skin from the nonwoven without difficulty, i.e., at these temperatures the lotion should be sufficiently viscous to detach from the nonwoven and transfer onto the skin. This temperature-dependent process can, however, lead to problems if the hygiene products are stored at relatively high temperatures, e.g., more than 30° C. In this case, it is frequently observed that the lotions “exude” on the nonwoven materials. It was therefore an object of the present invention to provide skin-friendly lotions for application to nonwoven materials for hygiene articles, where the storage stability of said lotions is to be ensured, in particular at high temperatures.
Furthermore, it is to be noted that the nonwoven in, e.g., baby diapers must be pervious to liquids and has therefore usually been prepared to be hydrophilic. Further finishing with a usually hydrophobic skin-friendly lotion could therefore reduce or significantly impair the transportation of liquid through the web into the absorbing materials.
Furthermore, it is desired that the lotions transfer as completely as possible from the nonwoven onto the skin of the wearer and, in this connection, optionally provide further additional uses, e.g., the reduction of odor formation or the growth of bacteria, fungi, and yeasts. In principle, it should be possible to apply the lotions to the nonwoven materials easily and to apply them as far as possible using the known preparation processes. It has been found that these properties could not be achieved in totality using the products of the prior art.
The lotion composition is typically applied to the absorbent article or a material intended to be used in such an article, in a molten state. This is normally done at a temperature between 35° C. and 100° C. Once the molten lotion has been applied it is allowed to cool and solidify to form solidified coating on the surface of the article or material onto which it has been applied. Any suitable application methods such as slot coating, extrusion coating, gravure coating, and spraying methods may be used.
One main problem when applying lotion compositions to absorbent articles or a material intended to be used in such articles is that the manufacturing process often is a very rapid process and the molten lotion will not solidify sufficiently before the article or material is folded or rolled up, resulting in smearing of the lotion. The lotion may further penetrate through, e.g., the topsheet of the absorbent article, onto which it has been applied, and migrate into the absorbent core making this hydrophobic and less absorbent.